Got it, no visual, just a path. Since splines have no collision, we cannot detect them with overlaps or traces. Technically, you could fetch them with Get Actor nodes and a Tag but that will require sorting by distance - if you have a lot of splines in the level, it may become tedious / awkward.
I’d still go with my original suggestion, a very simple spline mesh we do not render, only there to facilitate overlaps and procure a spline reference. Does this look like something you could work with:
Whenever we get close to the spline, we get its reference and the closest world location so we can hop on it and start following it along. The detection radius can be adjusted.
This runs on overlap, but can be set up to run on a timer or evoked with a player action instead:
And it will work with any number of splines.
Behind the scenes:
You can (should?) use a much simpler mesh, an extruded triangle with 3-4 loops might be enough. You may even get away with a plane.